Patent GB-1234989-A (GB)
Title: Resistive adjunct device and variable resistive component
IPC: H01C7/00
Filed: 1968-07-23
Abstract: 1,234,989. Printed circuit assemblies; variable resistors. BOURNS Inc. 23 July, 1968 [4 Dec., 1967], No. 35170/68. Headings H1R and H1S. A variable resistance unit is modified by mechanically and electrically integrating it with an adjunct resistance member which comprises a wafer of insulating material having on at least one surface thereof a resistance element electrically connected between the conductive areas which each extend into at least one of a plurality of apertures provided in the wafer into which terminal pins of the unit are disposed. The adjunct device 20, Fig. 1, comprises a ceramic wafer 20w, Fig. 3, provided with a plurality of apertures R<SP>1</SP>, G<SP>1</SP> 7<SP>1</SP>, B<SP>1</SP> arranged in a spatial array congruent with the terminal pin array R, G of a variable resistance unit 12 and the apertures in a circuit board, not shown. Disposed on the upper face of wafer 20w and continuing on into and through the holes are conductive films F1, F2, F3 applied by painting or silk-screening on the desired areas and interconnecting elements F2, F3 is a resistive film XI formed of a cermet composition or of conductive plastic material such as carbon-in-resin, carbon film, carbon and metal, metal films or metal nitrides. Each of the four apertures shown has affixed therein a metal eyelet which makes contact with the conductive films F1, F2, F3 on the walls of the apertures. The variable resistance unit 12 is assembled with the adjunct device by passing its terminals R, G through apertures R<SP>1</SP>, G<SP>1</SP> so that the pins R, G extend from the unit for plugging into the circuit board. One of the apertures B<SP>1</SP> is provided with a stub terminal B pin which extends below the lower face of the wafer but not above the upper face. As shown in Fig. 10, when the various parts are assembled the network of variable resistance 12, Z<SP>1</SP>, Z2 is modified to present a threeterminal network including element XI, terminals G, B being used as output terminals. The wafer may be provided with an insulating jacket I which covers the resistance elements and conductive films. Instead of using resistance coatings the resistance element may be in the form of a wire wound on a mandrel or card which is disposed on the surface of the wafer or in a cavity formed therein. In the embodiment of Fig. 11 and Figs. 4, 5, 6 (not shown), top and bottom faces of the wafer bear different patterns, i.e. resistance elements X2, X3 are arranged orthogonally on opposite faces of the wafer between the conductive films and eyelets of the apertures. With this arrangement a choice of two different resistance values are provided to be combined in parallel with the resistances Z1, Z2 depending in which orthogonal set of apertures the pins G, Y are fitted. In the arrangement of Fig. 12 and Fig. 7 (not shown), the variable resistance unit 12 is provided with three terminal pins R, G, Y which plug into apertures R<SP>1</SP>, G<SP>1</SP>, Y<SP>1</SP> of wafer 20, the fourth aperture B<SP>1</SP> being provided with a stub terminal pin B, the arrangement making available four terminal pins for connection to a switch. In the arrangement of Figs. 13, 8 (not shown), the variable resistance 12 is provided with three terminal pins which plug into holes R<SP>1</SP>, G<SP>1</SP>, Y<SP>1</SP>, a resistance being connected between holes R<SP>1</SP>, Y<SP>1</SP>. However, no stub terminal pin B is provided and this aperture forms no part of the circuit. One or more additional adjunct members may be mounted in a stack and assembled to a single variable resistance unit 12.